1. Field of the Invention
The present invention belongs to the technical field of electric equipment diagnosis, and relates to a method of harmonic diagnosis for electric equipment such as motors and inverters.
2. Description of the Related Art
Recent electric equipment has been tried to improve its productivity by a continuous and integrated production process. Furthermore, an energy saving device such as an inverter has been introduced together with a high-performing automated system in a wide range so as to achieve highly reliable equipment. Such mass production is being required in every industrial field.
Mass production equipment is generally operated continuously, and a breakdown (stoppage) in electric equipment often brings the entire process into a standstill. Once there is a breakdown, it not only damages production process but also loses the reliability of users, and may even cause a disaster. Thus, the downtime loss is immeasurable, and may lead to a fatal problem.
When they purchase brand new equipment (machine) and check it, enterprises perform the checking by making sure that the equipment (machine) operates according to its specification because at present there is no checking standards or unified rules. However, since recent automatic devices (machinery) have a combined system structure in which a lot of devices are connected via interface cables, there might be no matching between these systems, thus causing a lot of troubles later, or even fire accidents.
Furthermore, transportation equipment such as railroad trains and elevators to carry people are obliged to have a periodic inspection by statute; however, power conversion equipment (AC-AC converter) including motor equipment and inverters are checked only for the presence or absence of a temperature rise or abnormal noise, leaving safety problems unsolved.
The objects of diagnosing abnormalities and deterioration of the electric equipment include: to improve operation rate by reducing the downtime of the equipment; to reduce maintenance costs including material and labor costs; to reduce other costs by extending the replacement period and reducing the inspection maintenance; to prevent troubles; and to improve safety, reliability, productivity and quality.
Described above are the background and objects of the necessity of diagnosing abnormalities and deterioration of electric equipment. The conventional way of diagnosing abnormalities and deterioration in electric motors and inverters according to the present invention will be described in brief in the following sections 1 and 2.
1. Diagnosis of Abnormalities and Deterioration for Electric Motors
Methods of diagnosing abnormalities and deterioration for electric motors include: (1) vibration methods; (2) acoustic methods; (3) temperature methods; (4) torque methods; (5) current methods; and (6) waveform methods. Of these methods, vibration methods, which are the most frequently used methods, will be described as follows. The other diagnosing methods are omitted patents filed by the inventor of the present invention (Japanese Patent Applications No. 2000-386603, No. 2001-265949, No. 2001-358718, and No. 2003-030807).
Vibration methods have a simple diagnosis and a precise diagnosis. In the simple diagnosis, an abnormality is determined by a vibration overall value of a rotary machine in an electric motor or load equipment including an electric motor by installing a vibration pickup of electrokinetic type, piezoelectric type or displacement type as close to the source of vibration as possible. In the precise diagnosis, the cause and location of an abnormality and deterioration are determined by the frequency analysis of vibration. These diagnoses are both restricted to mechanical elements such as bearings and rotary shafts.
As described above, for the simple diagnosis, some enterprises have their own standards to determine between abnormality and normality by a vibration overall value based on the accumulated data and experience. However, most other enterprises depend on the ISO standard, the JIS standard or the VDI standard (the standard of the association of German Engineers). These standards, however, provide only average evaluations, and cannot be applied to all rotary machines. For example, the ISO standard and the JIS standard have ISO-2372 and JIS-B0906, respectively.
When an abnormality is determined by the simple diagnosis, a precise diagnosis is required to determine the cause and location. In general, vibration signals generated from rotary machines are complicated, and are hardly simple. In order to obtain significant information from the signals to precisely determine the presence or absence of an abnormality, frequency analyses are most widely used. Applying a frequency analysis to a vibration signal makes it possible to determine the cause and location of the abnormality.
For the rotary machines including these electric motors, the relation between the cause of an abnormality and the number of vibration events is not accurate because it is obtained from the data accumulated over a long period.
2. Diagnosis of Abnormalities and Deterioration for Inverters
Inverters have the advantages of saving energy, and improving productivity and operability so as to contribute to the achievement of high-tech industrial machines of various kinds. Inverters are now essential devices in motor equipment, and their production amount is increasing year by year. The production amount of industrial inverters in Japan in the fiscal year of 1999 exceeded 1,800,000 (equivalent to about 100 billion yen) according to MITI (present METI) Current Survey of Production.
By the way, an inverter is formed of a lot of parts including electronic parts such as ICs, resistors, capacitors and transistors, and other parts such as cooling fans and relays. These components cannot be used permanently, and their durable years greatly depend on the operating environment. Almost all the electronic parts have operating lives in compliance with Arrhenius law (the rule of doubling for every 10° C.: operating life doubles for every 10° C. reduction in the ambient temperature), so the inverter needs a periodic inspection.
As a diagnosis of abnormalities and deterioration for inverters, the JEMA (Japan Electrical Manufacturers' Association) recommends a periodic inspection in their guidebook “An encouragement of Periodic Inspection of General-Purpose Inverter” to prevent potential troubles.
However, in a diagnosis of abnormalities and deterioration for an inverter, the determination of the cause and location of an abnormality and deterioration requires the inverter to be stopped or even decomposed so as to be checked by a specialist with a special measuring device. In reality, inverters are often used until they are down. During the periods, the inverters often cause deterioration in their functions such as energy saving function and protection function, and also cause abnormalities in their output properties. In addition, the inverters often adversely affect other devices, such as causing robot malfunction or electric motor trouble.